The weapons called guns use the expansion of a gas to propel a projectile. The gas can take several forms, such as compressed air stored in a canister attached to the gun. Alternatively, fire arms are a sub-type of gun, and use the expansion of a gas created by combustion to propel a projectile.
A combustible material such as gun powder is stored within the projectile cartridge. A firing mechanism in the gun is used to ignite the combustible material. The combustion process creates the gas.
The heat of combustion increases the temperature of the gas, which causes it to expand to an area of lower pressure. The primary exit from the gun is through the open end of the gun barrel. As a result, the gas expands towards the open end of the gun barrel. That expansion is transferred to the projectile, propelling it out from the gun barrel.
The creation and expansion of the gas is a fast process. Accordingly, the projectile exits the gun barrel at high speed.
The generation and expansion of the gas also creates significant noise in the form of a blast wave.
That blast wave is undesirable for a number of reasons. Firstly, the blast wave creates a loud noise, which can damage a person's ears. Repeated exposure to blast waves will result in hearing loss. Secondly, the noise of the blast wave makes the use of guns unpleasant. That may be relevant where people use guns for recreational purposes such as target shooting. Thirdly, the blast wave can create a safety hazard. For instance, police may use guns around volatile gases such as those present in meth labs, or the flash and noise may attract enemy fire.
Devices called suppressors or silencers are used to control the gas expansion and thereby minimise the adverse effects it creates.
One common type of suppressor is a device which is configured to be attached to the end of a gun barrel. These devices include an inlet and an outlet, and a connecting passageway. In-use a projectile fired by the gun passes through the inlet, along the passageway, exiting the suppressor via the outlet.
These suppressors include a series of internal baffles which define chambers within the suppressor. The gas generated during firing of the projectile is able to expand into the chambers. The chambers are arranged such that a first chamber is comparatively larger than the volume of the gun barrel. Accordingly, the first chamber provides a large volume into which the gas may expand. The gas can subsequently expand into adjacent chambers in the suppressor. Together, the chambers facilitate a gradual expansion of the gas. As a result, the expansion of the gas is slower than were the suppressor not used, which minimises the noise created by the blast wave.
Another type of suppressor is provided by drilling holes in the gun barrel, and positioning a “can” or suppressor body about the gun barrel. The barrel and suppressor are therefore configured so that the expanding gasses are released sequentially into the suppressor body along a portion of the gun barrel's length. Obviously the bullet only comes out the end of the barrel, but gasses have the option of expanding into the suppressor body rather than exiting the end of the gun barrel.
All suppressors are designed to minimise any adverse affects on the passage of a bullet e.g. the suppressor does not alter the bullet's trajectory or reduce its velocity.
There are a number of different techniques known to construct suppressors. The most common technique is deforming sections of a rigid sheet material, and securing these together via welding. Alternatively components can be formed by machining of materials to form components that are then connected together by welding or fastening with threaded connectors. These techniques are often used to form the main (outer body) of the suppressor.
In yet another common manufacturing method a main, hollow body is first formed. Baffles are subsequently secured to the body using techniques such as welding, or using spacers and threaded retainers.
Another technique involves forming, casting or machining a mono-core baffle structure. This is subsequently secured within a hollow outer body.
However, all of the known techniques for manufacturing suppressors have disadvantages.
For instance, it is difficult to accurately position and weld baffles inside the main body of the suppressor. Even if a person has sufficient skill to secure the baffles in position then it is a time consuming and costly process.
Often, baffles are incorrectly positioned when assembled. This can lead to problems such as ineffective suppression of noise generated by the blast wave. Even worse, incorrect positioning of baffles can lead to baffle strike, where a projectile contacts the baffle. This is a health and safety issue and can injure the person using the gun as it would cause the projectile to travel in an unintended direction. It will also damage the suppressor and make it unusable.
In addition suppressors made as described above may not be sufficiently durable to withstand the common forces experienced in use. The weight of the various components may also increase the weight of the suppressor, hindering its ease of use.
Newly developed manufacturing techniques provide opportunities for manufacturing of suppressors. For instance, selective metal melting (“SMM”), and laser metal sintering (“LMS”) which is a sub-type of SMM, are three dimensional printing technique that can be used to manufacture different types of products, from a metal powder feed material
Both of SMM and LMS are additive layer manufacturing processes, that utilise a manufacturing apparatus to convert computer generated (CAD) models into three dimensional products. A metal powder is distributed onto a substrate/support, and a laser is directed onto at least a portion of the layer of powder. The laser heats the powder so as to fuse selected individual particles together to form a portion of the product.
The laser is then disengaged and a wiper is used to deposit another layer of metal powder. The laser is then again used to heat selected powder particles and fuse those together. The process is repeated to substantially create the required product.
LMS techniques have been used to manufacture components of suppressors. For instance, LMS has been used to construct baffles for a suppressor. In that situation, the baffles were secured to a spine. The spine and baffles were subsequently secured within a housing, and the housing was closed by attachment of end walls using techniques like welding. However, those products are limited because the individual components must subsequently be assembled. Therefore, the prior art has not maximised the efficiency of the manufacturing process.
In addition, the outer housing in which the spine/baffle structure was secured was not manufactured using LMS techniques. This indicates that manufacturing both the housing and internal baffles using LMS techniques was a difficult process, and not one which was easily achieved.
It is also possible that the baffles will not provide a complete seal to create appropriate cavities within the housing. As a result, the suppressors manufactured using these methods may not adequately control expansion of gases within the suppressor. As a result, those products are unlikely to function as an effective suppressor.
Furthermore, the creation of a spine involves redundant material. Therefore, the suppressors manufactured using LMS to produce separate components are unduly heavy. As a result they do not provide a completely satisfactory solution to the needs for manufacturing suppressors. Additive layer manufacturing processes, and particularly LMS, have a number of inherent issues which have inhibited their successful use in manufacturing of products such as suppressors.
In developing a method of manufacturing a suppressor, the inventor encountered several problems. For instance, the powdered material deposited must be supported before it is fused. The necessary supporting must be provided by the layer of material which has previously been fused. Insufficient support will likely result in the build failing. These problems are most relevant where a structure is being created that is not parallel to the build direction. This is a significant limitation on the design of products which can be manufactured using LMS technology.
Other problems include the creation of heat stress in the suppressor during melting of the deposited layers. These stresses create problems such as warping of the components of the suppressors, which meant hindered successful creation of a suppressor using LMS technology. This may be due to different components of the suppressor having different thicknesses, which means that the components react differently to the heat applied to fuse the deposited powdered material. This is a particular relevant in manufacturing suppressors, which are looking to maximise cavity volume, have sufficient strength to withstand the force of expanding gases, and minimise the suppressors total volume.
The inventor investigated existing applications in which LMS techniques have been utilised to produce complex products having a substantially closed internal cavity, and internal structures within the cavity, so as to assist in developing a suppressor design using LMS techniques. However, the issues of providing sufficient support for a layer of deposited material prior to fusing still required significant effort and inventive contribution to solve in the particular application of suppressors.
For instance, PCT Publication No. WO 2008/118973 describes how to manufacture a product having an internal baffle or structure. That product must be built from one of the four corners of the housing and having the housing at a 45° angle to the horizontal. That limits the orientation of the components that can be constructed inside the housing. In fact, the manufacturing techniques described in PCT Publication No. WO 2008/118973 would not enable construction of a suppressor having function baffles therein.
Accordingly, it would be advantageous to have an improved suppressor, and method of manufacture, which addresses any or all of the foregoing problems.
Alternatively, it is an object of the present invention to address the foregoing problems or at least to provide the public with a useful choice.
All references, including any patents or patent applications cited in this specification are hereby incorporated by reference. No admission is made that any reference constitutes prior art. The discussion of the references states what their authors assert, and the applicants reserve the right to challenge the accuracy and pertinency of the cited documents. It will be clearly understood that, although a number of prior art publications are referred to herein, this reference does not constitute an admission that any of these documents form part of the common general knowledge in the art, in New Zealand or in any other country.
Throughout this specification, the word “comprise”, or variations thereof such as “comprises” or “comprising”, will be understood to imply the inclusion of a stated element, integer or step, or group of elements integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.
Further aspects and advantages of the present invention will become apparent from the ensuing description which is given by way of example only.